What is the Kothari formula used for in calculating blood transfusion requirements in adult or pediatric patients with a history of anemia or other conditions affecting blood loss, undergoing major orthopedic surgeries such as hip or knee replacements or spinal surgeries?

Kothari Formula for Blood Loss Calculation

The Kothari formula is not a recognized or validated method for calculating blood transfusion requirements in orthopedic surgery—the evidence-based literature does not reference this formula, and you should instead use established methods like the Gross equation, hemoglobin balance, OSTHEO formula, or hemoglobin-dilution method for estimating perioperative blood loss.

What the Evidence Actually Shows

The available research identifies four validated methods for calculating blood loss in orthopedic surgery, but the "Kothari formula" is not among them. 1 A comparative study of 245 patients undergoing total knee arthroplasty evaluated the Gross equation, hemoglobin (Hb) balance, the Orthopedic Surgery Transfusion Hemoglobin European Overview (OSTHEO) formula, and Hb-dilution method—finding that the Hb-balance method had the highest combined correlation coefficient and may be the most reliable method. 1

Recommended Blood Loss Calculation Methods

For Length of Stay Prediction

• Use Bourke's formula if your primary interest is associating blood loss with length of stay, as it correlates significantly with this outcome. 2

For Transfusion Risk Prediction

• Use Liu's or Meunier's formula if your primary interest is calculating the risk of blood transfusion, as these correlate most strongly with transfusion incidence. 2
• The formulae of Mercuriali and Lisander are becoming redundant in contemporary practice. 2

General Blood Loss Estimation

• The hemoglobin balance method demonstrated the highest reliability in a head-to-head comparison of calculation methods for total knee arthroplasty. 1
• Blood volume can be calculated using Moore or Nadler formulae, which show very strong correlation with each other. 2

Practical Blood Ordering Approach

Preoperative Assessment

• Screen for anemia at least 4 weeks before elective surgery to allow time for evaluation and treatment. 3
• Assess iron status with serum ferritin and transferrin saturation (TSAT), diagnosing iron deficiency when ferritin <30 μg/L and/or TSAT <20%. 3
• In the presence of inflammation, ferritin <100 μg/L with TSAT <20% indicates iron deficiency. 3

Blood Ordering Schedule

• Use the surgical blood ordering equation rather than arbitrary formulas to determine crossmatch requirements. 4
• Calculate the crossmatch to transfusion ratio (C:T)—ratios higher than 2.5 indicate excessive crossmatching. 4
• For procedures with calculated red blood cell units less than 0.5, implement a group and save policy rather than routine crossmatching. 4

Expected Blood Loss in Hip and Knee Surgery

Hip Arthroplasty

• Median estimated blood loss is approximately 984 mL. 5
• Transfusion rate is approximately 18% when tranexamic acid is used routinely. 5
• Preoperative hemoglobin concentration is the only independent predictor of red blood cell transfusion. 5

Knee Arthroplasty

• Median estimated blood loss is approximately 789 mL. 5
• Transfusion rate is approximately 11% when tranexamic acid is used routinely. 5
• Low preoperative hemoglobin, low body mass index, and prolonged operation time independently predict transfusion requirements. 5

Critical Pitfall to Avoid

Do not use linear formulas that assume all blood lost contains the initial hemoglobin concentration—these underestimate allowable pretransfusion blood loss because they fail to account for hemodilution during surgery and preoperative fluid administration. 6 More sophisticated calculations that account for blood volume expansion and progressive hemodilution provide more accurate estimates. 6